The invention relates to a method and a device for the non-invasive measurement of the blood pressure and for simultaneous detection of arrhythmia.
The clinical standard of measuring the arterial blood pressure is the auscultation of audible sounds during the release of an inflated cuff in the cubital region of the brachial artery. The method is called the Riva/Rocci method by analysis of the so-called Korotkoff pulse sounds. First, non-invasive blood pressure measuring devices automatically recorded the Korotkoff sounds by the integration of a microphone into the cuff design. Although these devices proved to be very accurate, the critical microphone positioning and the occurrence of artefact sounds limited the clinical use of this method. Detection of arrhythmia proves to be an important parameter for prevention of cardiac diseases. It is known in the art to determine arrhythmic activities by means of an electrocardiographic method. Since both arrhythmia and chronic hypertension is associated with a severe risk in establishing cardiovascular diseases such as arteriosclerosis and cerebral ischaemia, it is known to simultaneously measure the blood pressure of the patient and to detect arrhythmic activities by the use of an electrocardiogram.
From U.S. Pat. No. 4,262,674 it is known, to simultaneously measure the blood pressure based on Korotkoff sounds and to determine time differences between two consecutive pulses. The method according to this US patent is difficult to carry out because of the mentioned critical microphone positioning and the occurrence of artefact sounds. Further, the method according to the US patent is based on a strict consecutive treatment of measured pulses. The procedure does not analyse the total pulse pattern during the measuring time.
The oscillometric non invasive measurement of the arterial blood pressure has been clinically introduced at the beginning of the 1980s. The technology required a pneumatic pressure pulse detecting system and a microcomputer based signal analysis. Due to the fast technological progress on semiconductors, the devices were consequently equipped with smaller but more powerful microcomputers, programs and memories. In that way, the accuracy and stability of the non-invasive arterial blood pressure measurement was gradually improved.
The oscillometric method does not detect pulse sounds, but pressure changes within the cuff during the deflation process. The pressure pulses are generated by small amounts of streaming blood passing the vessels under the partially inflated cuff. Oscillometric devices avoid the use of a microphone and just require the application of a cuff at the patient""s application site. For that reason, this technology was not only widely introduced clinically but was further integrated within a growing number of small blood pressure measuring devices, built for home use application.
Non-invasive oscillometric arterial blood pressure measuring units for home use were introduced widely towards the end of the 1980s. These devices measure and display three values: the arterial systolic pressure, the arterial diastolic pressure and finally the pulse frequency; all parameters are derived from the cuff application site.
The medical relevance of these devices is high. They are used in persons for whom regular measurements are recommended as a preventative measure, as well as in patients undergoing hypertensive or hypotensive blood pressure treatment. Since the age-dependent prevalence of hypertension is very high within the industrialised countries, regular blood pressure measurement serves as a crucial diagnosis measure to supplement the physician""s diagnostic results.
As chronic hypertension is associated with a severe risk in establishing certain cardiovascular diseases, e.g. arteriosclerosis and cerebral ischaemia, a physiological adjustment of the arterial blood pressurexe2x80x94especially the diastolic arterial blood pressurexe2x80x94has been recognised as a highly efficient risk reduction of such disorders.
Further, a broad range of cardiac and extra-cardiac diseases are accompanied by rhythm disorders of the heart. This applies e.g. for diseases of the coronary arteries, diseases of the myocardial muscle, and disorders of the heart""s excitation. In some cases, arrhythmia are significant early symptoms indicating the increased risk of developing certain severe heart malfunctions.
Some relevant arrhythmic heart activities are characterised by pathological variations of peripheral pressure pulse curves. So, pressure pulse curves may be used to identify certain arrhythmic events of the heart. Since pressure pulsations are monitored in the course of the oscillometric measurement, the analysis of the pulse pattern may be used to identify arrhythmic events. The analysis of the pulse rhythm is based on the analysis of pulse time difference, which is the time span between two correspondent pulse characteristics.
In case of a pathological rhythm status, pulse time differences may vary significantly in the course of the NIBP (xe2x80x9cnon-invasive blood pressurexe2x80x9d) measurement, or may be basically beyond physiological ranges. That means pulse time differences either change significantly or prove to be too high or too low. This is the basis of the detection of clinical relevant arrhythmia activities:
Supraventricular premature contractions: variation high due to pulse loss
Ventricular premature contractions: variation high due to pulse loss
Atrial fibrillation variation high due to absolute arrhythmia
Paroxysmal supraventricular tachycardia mean time difference low
Sinus-Tachycardia mean time difference low
Sinus-Bradycardia mean time difference high
Ventricular Bradycardia mean time difference high
Some arrhythmic activities are unfortunately not noticed by patients, since the associated symptoms remain minimal. However, certain types indicate a severe forthcoming heart malfunction. For this reason, early diagnosis and therapy may diminish the risk of serious complications.
Arrhythmia are very common within the population of industrialised countries. For example about 0.5% of all adults, 3% of all people aged over 60, and 15% of all people over 70 suffer from atrial fibrillation.
It is an object of the present invention to overcome the drawbacks of the prior art, especially to provide a device and a method for simultaneously measuring blood pressure and detecting arrhythmic activities, which are both reliable and easy to apply, which are adapted for home use and which are easy to manufacture and carry out.
According to the present invention, these objects are solved with a method and a device according to the independent patent claims.
According to the invention, a pulse distribution is measured and is analysed by the device. The pulse distribution is investigated by using known medical criteria representing physiological or pathophysiological conditions, which are stored within the device. These criteria decide whether there is reason to diagnose an arrhythmic activity in the course of the NIBP measurement. Transformation, calculation and comparison can be effected analogically, digitally or by direct EDP comparison of curves. There can be signal storage and batchwise processing or on-line processing.
According to the method of the present invention, the blood pressure is preferably measured by measuring the pressure pulses of the blood in an artery by oscillometric measurement techniques. Measurement and analysis of the pressure pulses by oscillometric techniques allows the calculation of the blood pressure, especially the systolic and diastolic pressures. In order to indicate an arrhythmia, all values of the time difference between consecutive pulses are determined. The values of a plurality of consecutive pulse time differences are stored in a storing unit. The distribution of the pulse time differences is subsequently calculated in a calculating unit. In order to determine the existence of arrhythmic activities, the values and the distribution of the pulse time differences are compared with predetermined reference values and predetermined reference distributions of the pulse time differences in a comparing unit. In order to indicate the existence of arrhythmic activities, the comparing unit is caused to generate a signal if the values and/or distributions of the pulse time differences on the one hand and the predetermined arrhythmic specific values and distributions on the other hand are sufficiently close to each other. The signal can be optical, acoustic or any other kind of signal.
The method according to the invention is intended for a broad range of medical use. This includes the clinical application, the emergency based application, as well as home use. The indication of existence of arrhythmic activities tells the patient to consult a physician for a more detailed cardiac diagnosis.
The pressure pulse signals acquired by the oscillometric measurement are preferably amplified in a pulse pressure amplifier which generates an amplified signal. The amplified signal can subsequently be filtered and converted into a digital signal with an analogue/digital converter. Amplification and A/D conversion is known to those skilled in the art and is not the object of the present invention.
In a preferred embodiment, a pulse time difference histogram is generated in the calculating unit. Representation of the pulse time difference distribution in a histogram allows an especially reliable and precise detection of tie existence of arrhythmic activities.
The device according to the present invention substantially comprises a blood pressure monitor for indicating the blood pressure values and a cuff for the non-invasive oscillographic measurement of the blood pressure. The cuff is connected to the blood pressure monitor. A time difference measuring unit is used to determine the values of time pulse differences between two consecutive pulses. The device further comprises a storing unit for storing a plurality of consecutive time pulse differences which have been determined by the time difference measuring unit. The device is further provided with a calculating unit for calculating a statistic distribution of the time pulse differences and a comparing unit for comparing the values and the statistic distribution of the time pulse differences with predetermined reference values and reference distributions. The comparing unit is adapted to create a signal when the value and/or the distribution of the time pulse differences on the one hand and the predetermined value or reference distribution representing pathophysiological conditions on the other hand are sufficiently close to each other. It is also conceivable to create a signal if the difference between the measured parameters and criteria representing physiological values exceeds a certain amount.
The device comprises preferably a pulse pressure amplifier which creates an amplified pulse signal. The device further comprises a signal filter and optionally an A/D converter which filters and converts the amplified signal into a digital signal. The calculating unit is adapted to calculate a pulse time difference histogram. Such calculating units are known to those skilled in the art and are not the object of the present invention.
The device is preferably provided with indication means for indicating the existence of arrhythmia. Any kind of known indication means are possiblexe2x80x94preferably, for instance, signal lamps, LEDs or an LCD display. It is also conceivable to provide acoustic indication means.
The apparatus detects arrhythmic activities during the non-invasive measurement of the arterial blood pressure. The apparatus uses a cuff which is wrapped around the patient""s upper leg, lower leg, toe, upper arm, forearm or finger. After inflation of the cuff, the pressure is released gradually in order to measure arterial pulses by detecting pressure pulses. An inbuilt memory stores the pulse amplitudes of each pulse, the associated cuff pressure and the time differences between two consecutive pulses. While the first and second parameters are used to determine the systolic, mean and diastolic arterial blood pressure, the third parameter is applied in order to detect arrhythmic pulse activities of the patient. The detection includes premature ventricular and supraventricular contractions, absolute arrhythmia as well as tachycardia and bradycardia. The apparatus displays the result of the rhythmic analysis and indicates the user to take actions according to the result.
The analysis of the pulse time difference within a oscillometric measurement discloses the mean pulse time difference and the scattering of pulse time differences within one complete measurement cycle. Therefore the pulse time differences are investigated for every full measurement in order to detect possible arrhythmic activities.
The present invention analyses the pulse time difference signals derived from pulses within the pulse oscillogram. The analysis result is displayed beside the conventional values.